This research proposal is concerned with the process of polyadenylation in mouse. The specific objectives of the proposed research are: (a) Identification of the DNA sequences specifying the site of polyadenylation, (the polyadenylation signal) and (b) Reexamination of the requirement for polyadenylation in the biogenesis of mRNA, in vies of recent observations from our lab (see Preliminary Results). The experimental approach comprises in vitro reconstitution of genes, reintroduction into the mouse chromosomes by transfection and analysis of the corresponding RNA species. The high measure of flexibility afforded by in vitro gene reconstitution experiments is considered to confer a major advantage to a successful completion of this research proposal.